JP2017067479A - Measurement device and measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measurement device and a measurement method that are advantageous in terms of measurement accuracy and measurement time.SOLUTION: Provided is a measurement device for measuring the shape of an object to be measured, the measurement device having: projection means for projecting a first pattern light or a second pattern light to the object to be measured; image-capturing means for acquiring the image data of the object to be measured; a control unit for controlling the projection means and the image-capturing means; and acquisition means for acquiring information relating to the cycle of intensity of a light other than the pattern lights radiated to the object to be measured, a first condition including a combination of pattern lights, the number of times images are captured by the image-capturing means, and an interval between image captures, a second condition including the same image-capture count and image-capture interval as in the first condition and a reversed combination of the first pattern light and second pattern light, the control unit exercising control based on the first condition and second condition inserting a time interval that is an integral multiple of the cycle, finding the intersection position of gradation values of corresponding image data in correlation to image data acquired by each condition in order of image captures, and calculating the shape of the object to be measured on the basis of the intersection position.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a measuring device and a measuring method.

  As an apparatus for measuring the shape of an object to be measured, an optical measurement apparatus using a pattern projection method is known. In the pattern projection method, a predetermined pattern light is projected onto an object to be imaged, a pattern is detected from the imaged data, and distance information at each pixel position is calculated from the principle of triangulation, so that the object to be measured is detected. Seeking shape. As the pattern projection method, a spatial encoding method is often used in which a pattern light having alternating bright and dark lines is projected to binary-encode the space. In order to improve the measurement accuracy by the spatial encoding method, it is necessary to accurately determine the boundary between the bright part and the dark part from the obtained imaging data.

  As a method for accurately determining the boundary between the bright part and the dark part, the first pattern light having the bright part and the dark part alternately and the relationship between the bright part and the dark part of the pattern light are inverted, and the first pattern There is a method of projecting a second pattern light having a complementary relationship with light and determining the intersection as a boundary. As long as each pattern light has a complementary relationship and the same plane is measured, the distance between the intersections and the width of the bright portion (or the width of the dark portion) coincide. However, in actual measurement, the complementary relationship may be lost due to the influence of ambient light (indoor light such as a fluorescent lamp), and the position of the intersection may be shifted. It cannot be distinguished whether the deviation of the intersection position is caused by ambient light or the shape of the object to be measured. As a result, the measurement accuracy is degraded. As a method of reducing the influence of ambient light, a method of reducing the influence of ambient light by synchronizing the imaging timing with a period that is an integral multiple of the commercial power supply frequency (50 Hz, 60 Hz), which is the main frequency of a fluorescent lamp, is known. (Patent Document 1).

JP 2009-19884 A

  However, the invention described in Patent Document 1 has a waiting time for synchronization of imaging timing, which may be disadvantageous in terms of measurement time.

  An object of the present invention is to provide a measurement device and a measurement method that are advantageous in terms of measurement accuracy and measurement time, for example.

In order to solve the above problems, the present invention is a measuring device for measuring the shape of an object to be measured,
Projection means for projecting the first pattern light having the bright part and the dark part or the second pattern light in which the bright part and the dark part of the first pattern light are inverted onto the measurement object, and the pattern light is projected An imaging unit that captures an image of the measurement object, acquires image data, a control unit that controls the projection unit and the imaging unit, and information on a period of intensity of light other than the pattern light emitted to the measurement object. The first condition includes a combination of the first pattern light and the second pattern light projected by the projection unit onto the object to be measured, the number of times of imaging by the imaging unit, and the imaging interval, The conditions include the same number of imaging and imaging interval as in the first condition, a combination in which the combination of the first pattern light and the second pattern light is switched, and the control unit performs projection by the projection unit in the first condition and For imaging means The projection unit and the imaging unit are configured to start imaging by the projection unit and start imaging by the imaging unit under the second condition with a time interval that is an integral multiple of the period of the intensity of light other than the pattern light. The image data acquired under the first condition and the image data acquired under the second condition are associated with each other in the imaging order of the respective conditions to determine the intersection position of the corresponding gradation values of the image data, and the calculated intersection position Based on this, the shape of the object to be measured is calculated.

  According to the present invention, for example, it is possible to provide a measuring apparatus and a measuring method that are advantageous in terms of measurement accuracy and measurement time.

It is a figure which shows the measuring device which concerns on 1st Embodiment, pattern light, and light intensity distribution. It is a figure explaining the influence by environmental light. It is a figure which shows the imaging timing chart which concerns on 1st Embodiment. It is a graph which shows that tact time is shortened.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1A is a schematic diagram illustrating a configuration of a measurement apparatus according to the present embodiment. FIG. 1B and FIG. 1C show the first pattern light having bright portions and dark portions alternately and the second pattern light in which the relationship between the bright portions and the dark portions of the first pattern light is reversed. FIG. FIG. 1D shows a gradation value distribution when the first pattern light and the second pattern light are projected onto the reference plane. The measurement apparatus according to the present embodiment includes a head 10, a control unit 3, and a calculation unit 4. The head 10 includes a projection unit 1 and an imaging unit 2. The projection unit 1 includes a light emitting unit 5, a pattern setting element 6 and a projection optical system 7, and the imaging unit 2 includes an imaging lens 8 and a sensor element 9. The direction in which the pattern light is projected onto the measurement object 20 is defined as the z axis, and the axes orthogonal thereto are defined as the x axis and the y axis, respectively.

  The projection unit 1 sets (forms) the light emitted from the light emitting unit 5 to the pattern light 15 by the pattern setting element 6 and projects the light onto the measurement object 20 via the projection optical system 7. As the pattern setting element 6, a liquid crystal element, DMD (digital mirror device), or the like is used, and it is possible to set (select) an arbitrary pattern light. The light emitting unit 5 preferably has a light emitting element such as an LED or a combination of the light emitting element and a uniform illumination system for reducing luminance unevenness. The imaging means 2 captures the measurement object 20 onto which the pattern light 15 is projected by guiding light from the measurement object 20 to the light receiving surface of the sensor element 9 by the imaging lens 8 and acquires image data. The sensor element 9 is preferably a photoelectric conversion element such as a CMOS or CCD. The light emitting unit 5, the pattern setting element 6, and the sensor element 9 are controlled by the control unit 3, and light emission, pattern setting, and imaging are performed at arbitrary timings, respectively.

  The arithmetic unit 4 stores the gradation value (luminance) data of the image data captured by the imaging unit 2 corresponding to the pixels. Since the relationship between the relative position and orientation of the projection unit 1 and the imaging unit 2 is known in advance, the coordinates of the points on the surface of the measurement object 20 are calculated by the calculation unit 4 based on triangulation, and the measurement target is measured. The shape of the object 20 is required. When calculating the coordinates of a point on the surface of the measurement object 20, at least one set of pattern light 15 is projected, and each gradation distribution (luminance distribution) is imaged by the imaging means 2. One of the pattern lights 15 is first pattern light having a bright part and a dark part shown in FIG. The other is the second pattern light shown in FIG. 1C, in which the relationship between the bright part and the dark part is inverted with respect to the first pattern light, that is, in a complementary relation with the first pattern. is there. Assuming that the first pattern light and the second pattern light are irradiated onto a plane serving as a measurement reference, the gradation distribution is as shown in FIG.

  The calculation unit 4 has an intersection C between the first gradation distribution P on which the first pattern light shown in FIG. 1D is projected and the second gradation distribution N on which the second pattern light is projected. Is calculated. In the case of the present embodiment in which the ratio of the bright part to the dark part of the first pattern light and the second pattern light is 1: 1, if the intersection C is detected with respect to the reference plane, the intersection C is equal. It becomes pitch. When the measurement object 20 is measured, the intersection C is displaced from the equal pitch position by the shape of the measurement object 20 with respect to the reference plane. Using this displacement, the z-coordinate of the measurement object 20 is calculated.

  Next, the influence of light (environment light) irradiated on the measurement object 20 in addition to the pattern light will be described. Ambient light such as a fluorescent lamp (illumination lamp) in the measurement environment (space) in which the measurement object 20 is arranged flickers according to the frequency (50 Hz, 60 Hz, etc.) of the power source, and the intensity varies. FIG. 2A shows a temporal change in ambient light intensity and an imaging timing chart in the comparative example. The period of ambient light intensity and each imaging timing are not synchronized. FIG. 2B shows the gradation distribution and the intersection obtained at the imaging timing (imaging interval) shown in FIG. FIG. 2C shows a temporal change in ambient light intensity and an imaging timing chart when imaging is performed in synchronization with the cycle of ambient light.

  2A, the first pattern and the second pattern are expressed as P and N, respectively, and the imaging order is expressed as n1, n2,..., N12. For example, the pattern imaged at n1 is the first pattern. The ambient light intensity varies with time. In FIG. 2B, the odd number 2i-1 (i is a natural number) in the imaging order is the first pattern, the even number 2i is the second pattern, and the 2i-1th image and the 2ith image are captured. This is an example in which an intersection point is detected with respect to a reference plane in a pattern. When the ambient light intensity is sufficiently smaller than the intensity of the pattern light 15, the intersections are at an equal pitch as described above. However, when the ambient light is large and each imaging timing is not synchronized with the period of the ambient light intensity, an offset of the ambient light occurs in the output value. Therefore, as shown in FIG. 2B, the position of the intersection is shifted from the equal pitch. The deviation (error) from the equal pitch due to the ambient light is indistinguishable from the deviation from the reference plane due to the shape of the measurement object 20. Therefore, there is a possibility that a measurement error occurs due to the ambient light. As a method for avoiding this, as shown in FIG. 2C, a method of imaging in synchronization with the period of ambient light intensity is known (Patent Document 1). Occurs and the measurement time increases.

  FIG. 3 shows an imaging timing chart according to the present embodiment. As in FIG. 2A, the first pattern and the second pattern are expressed as P and N, respectively. In the present embodiment, the control unit 3 controls the projection unit 1 and the imaging unit 2 according to the first condition and the second condition. Each condition includes a combination of the first pattern P and the second pattern N, the number of times of imaging, and an imaging interval. A pattern group to be imaged under the first condition is a first group G1, and a pattern group to be imaged under the second condition is a second group G2. The imaging order in the first group G1 is n1, n2,..., N6, and the pattern to be imaged at each timing is {P, P, N, N, P, P} (first acquisition step). The imaging order in the second group G2 is p1, p2,..., P6, and the pattern to be imaged at each timing is {N, N, P, P, N, N} (second acquisition step). The control unit 3 controls the pattern setting element 6 and the sensor element 9 so that the pattern imaged at the timing ni and the pattern imaged at the timing pi have a complementary relationship.

The time interval between the starting time t _p1 in the second acquisition step of acquiring image data according to starting time t _n1 and the second condition of the first acquisition step of acquiring image data in accordance with the first condition, the intensity of the ambient light It is set to an integer multiple (γ times) of the period T0. However, depending on the accuracy determined by the clock mounted on the control unit 3 and the calculation accuracy in the calculation unit 4, it does not exactly coincide with γ times the period T0 of the ambient light intensity. the difference between the imaging start time t _p6 of t _p1 and timing n6 is at least the minimum period of the sensor element 9 (maximum sampling number less), and as γ is minimized, determines the γ and the minimum period of the sensor Is preferred. Further, the period T0 of the intensity of the ambient light may be obtained by measuring the ambient light in advance. Moreover, if it is a light source which depends on commercial frequencies (50 Hz, 60 Hz), such as a fluorescent lamp and a mercury lamp, you may obtain | require from the reciprocal number of the integral multiple of a commercial power supply frequency (50 Hz, 60 Hz). Further, the frequency for each power source may be measured in order to reduce the error due to the commercial power frequency generated for each power source. An acquisition means (not shown) acquires the frequency of the intensity of ambient light.

  The control unit 3 controls the sensor element 9 so that the measurement interval (imaging interval) of each timing in the first group G1 is equal to the measurement interval of each timing in the second group with the above-described accuracy. That is, the sensor element 9 is controlled so that the corresponding timings between the groups are equal to each other with the above-described accuracy. Here, the measurement interval of each timing within one group may be an unequal interval, and may be a desired measurement interval that is not limited by an integer multiple of the period T0 of the ambient light intensity, but the minimum period that can be realized by the sensor element 9 The most preferable form is determined by

  The calculation unit 4 performs an intersection detection calculation process in association with the imaging order of the first group G1 and the imaging order of the second group G2. For example, the intersection detection processing is performed by associating n1 with p1. Here, it is possible to perform the averaging process after detecting the intersections a plurality of times first, or after first averaging the first pattern image and the second pattern image, respectively. May be issued. The shape of the measurement object 20 is calculated based on the intersection position (shape calculation step).

  According to the control by the control unit 3 described above, the amount of ambient light is equal in one set of images (for example, a set of images captured at timing n1 and p1) that perform intersection detection. That is, the influence of ambient light can be reduced and measurement errors can be reduced. Furthermore, if the group interval (time interval) T2 and the measurement intervals within each group (ni + 1 and ni measurement intervals, pi + 1 and pi measurement intervals) are suitably controlled, the measurement time can be shortened.

  As described above, according to this embodiment, it is possible to provide a measuring apparatus and a measuring method that are advantageous in terms of measurement accuracy and measurement time.

(Second Embodiment)
Next, a measuring apparatus according to the second embodiment of the present invention will be described. The present embodiment is characterized in that the measurement interval T1 in the group is a constant value (period). The timing interval (imaging interval) in the first group G1 and the second group G2 is T1, the period of the ambient light intensity is T0, and the number of measurements in the first group G1 and the second group G2 is M. The condition of the group interval T2 in which the influence of the ambient light is reduced is as follows: M × T1 (total imaging time of the first group G1) is divided by the period T0 of the ambient light intensity, and an integer α rounded up to the nearest decimal point is This is a condition that satisfies (1).
T2 = γ × T0 ≧ α × T0 (1)
Here, γ is an arbitrary integer. Expression (1) is an expression that defines the imaging start timing of the second group G2. Furthermore, considering the reduction in measurement time, the group interval T2 that satisfies the following equation (2) for the integer β rounded up after the decimal point of T1 / T0 reduces the influence of ambient light and shortens the measurement time. It is a condition to do.
T2 = γ × T0 <M × β × T0 (2)
Moreover, the relationship of following formula (3) is derived | led-out from Formula (1) and Formula (2).
α ≦ γ <M × β (3)
By setting an integer γ that satisfies Equation (3), it is possible to reduce both the influence of ambient light and the measurement time. In the present embodiment, the imaging cycle T1 may be controlled by the control unit 3 or may be controlled by the internal clock of the sensor element 9. The control of the group interval T2 is preferably given as a trigger signal from the control unit 3 to the sensor element 9.

  FIG. 4A is a graph showing a waiting time (tact time) in which imaging is not performed in order to synchronize with the environmental light period when the imaging period T1 is smaller than the environmental light intensity period T0. The horizontal axis represents the number of times of imaging (M ≧ 2), and the vertical axis represents the tact time (msec). In this example, the period T0 of the ambient light intensity is set to 10 msec, and the imaging period T1 is set to 3 msec. The solid line in the figure represents the tact time according to the present embodiment, and the wavy line in the figure represents a conventional example. As can be seen from FIG. 4A, the tact time is shorter in this embodiment at any number of measurements. It can also be seen that the effect of shortening the tact time is greater as the number of measurements is larger.

  FIG. 4B is a graph showing the tact time when the imaging period T1 is larger than the period T0 of ambient light intensity. In this example, the ambient light period T0 is 10.1 msec, and the imaging period T1 is 15 msec. As in FIG. 4A, it can be seen that the tact time is shorter in this embodiment at any number of measurements. It can also be seen that the effect of shortening the tact time is greater as the number of measurements is larger. As described above, according to this embodiment, it is possible to provide a measuring apparatus and a measuring method that are advantageous in terms of measurement accuracy and measurement time.

(Third embodiment)
Next, a measurement apparatus according to the third embodiment of the present invention will be described. In the second embodiment, the group interval T2 and the imaging cycle T1 are controlled by separate signals. The present embodiment is characterized in that these can be controlled by a trigger signal from the same control unit 3 or an internal clock of the same sensor element 9. First, assuming that the minimum sampling period (shortest imaging interval) of the sensor element 9 is T1 ′, an imaging period T1 that satisfies the following formula (4) is set with respect to an integer η rounded up from the decimal point of M × T1 ′ / T0.
T1 = η × T0 / M (4)
Here, the minimum sampling period T1 ′ in the present embodiment refers to the sampling due to the projection brightness of the projection means 1, the necessary exposure time derived from the reflectance of the measurement object 20, and the electric circuit of the sensor element 9. This is the time that takes into account the period. Next, a group interval T2 that satisfies the following formula (5) is set.
T2 = M × T1 = η × T0 (5)
As indicated by this equation, the group interval T2 is a multiple of the imaging cycle T1, and therefore, these can be controlled by the trigger signal from the same control unit 3 or the same internal clock of the sensor element 9.

  For example, when the period T0 of the ambient light intensity is 10 msec, the number of times of measurement M = 7, and the minimum sampling period T1 ′ of the sensor element 9 is 3 msec, T1 = 4.29 msec based on the equations (4) and (5). , T2 = 30 msec. According to this example, the conventional measurement time of 140 msec is 60 msec, and the tact time is shortened by about 60%. In other words, the number of measurements can be increased in the same measurement time as in the past (M = 16 in this example), and the S / N ratio can be improved by the averaging effect.

  As described above, according to the present embodiment, it is possible to obtain the effects of reducing the influence of ambient light and shortening the tact time as compared with the prior art by easy control. Although T1 ′ is the minimum sampling period, the present invention is not limited to this as long as the conditions described in the above embodiments are satisfied.

  In the above embodiment, the total imaging time is divided into two groups, but even when divided into four or more even groups, there is essentially no difference from the present invention, and the effect of the present invention does not change. . Further, the first group and the second group need not be continuously imaged. For example, even if the third pattern is imaged between the first group and the second group, the effect of the present invention does not change. .

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

DESCRIPTION OF SYMBOLS 10 Head 1 Projection means 2 Imaging means 3 Control part 4 Calculation part

Claims (5)

A measuring device for measuring the shape of an object to be measured,
Projecting means for projecting the first pattern light having a bright part and a dark part or the second pattern light in which the bright part and the dark part of the first pattern light are inverted onto the object to be measured,
Imaging means for imaging the object to be measured on which the pattern light is projected and acquiring image data;
A control unit for controlling the projection unit and the imaging unit;
Obtaining means for obtaining information on a period of intensity of light other than the pattern light irradiated on the object to be measured;
The first condition includes a combination of the first pattern light and the second pattern light projected onto the measurement object by the projection unit, the number of times of imaging by the imaging unit, and an imaging interval.
The second condition includes the same number of imaging and imaging interval as the first condition, a combination in which the first pattern light and the second pattern light of the combination are switched,
The control unit starts projection by the projection unit and imaging by the imaging unit under the first condition, and sets the second condition with a time interval that is an integral multiple of a period of the intensity of light other than the pattern light. Controlling the projection means and the imaging means so as to start projection by the projection means and imaging by the imaging means,
The image data acquired under the first condition and the image data acquired under the second condition are associated with each other in the imaging order of the conditions to determine the intersection position of the corresponding gradation values of the image data, and based on the calculated intersection position A measuring apparatus for calculating a shape of the object to be measured. When the imaging interval is a constant value T1, the imaging count is M, the light period is T0, and the time interval is T2, an integer α obtained by rounding up the decimal point of M × T1 / T0. And an integer β rounded up to the nearest decimal place of T1 / T0,
M × β × T0> T2 ≧ α × T0
2. The measurement apparatus according to claim 1, wherein control based on the first condition and the second condition is performed with a T2 that satisfies the condition. An integer obtained by rounding up the decimal point of M × T1 ′ / T0 when the imaging interval is a constant value T1, the shortest imaging interval of the imaging means is T1 ′, the imaging count is M, and the light period is T0. For η, T1 is
T1 = η × T0 / M
The measurement apparatus according to claim 1, wherein:   4. The measuring apparatus according to claim 1, wherein a period of intensity of light other than the pattern light is a reciprocal of an integral multiple of a commercial power supply frequency. 5. A measurement method for measuring the shape of an object to be measured,
A combination of a first pattern light having a bright part and a dark part and a second pattern light in which the bright part and the dark part of the first pattern light are inverted, the number of times of imaging, and an imaging interval; A first acquisition step of acquiring image data of the measurement object according to a first condition including:
From the first acquisition step, a time interval that is an integral multiple of the period of the intensity of light other than the pattern light irradiated to the object to be measured is set to the same number of imaging and imaging intervals as in the first condition, and the combination A second acquisition step of acquiring image data of the object to be measured according to a second condition including a combination in which the first pattern light and the second pattern light are interchanged;
The intersection position of the gradation value of each image data obtained by associating the image data acquired in the first acquisition step and the image data acquired in the second acquisition step in association with the imaging order of each condition and corresponding. And a shape calculating step for calculating the shape of the object to be measured based on the measurement method.

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